An issue with fluctuating lights - all lights

[OregonNed]

I haven't driven my truck a lot since I bought it last December - but last night I noticed an issue. Driving home from two cruise-ins yesterday I visibly noticed every light in the truck intermittently dimming and brightening. When the lights appear "normal", the gauge seem to be sitting between 12-13 volts - but in the "bright" phase, the gauge jumps to 16-18 volts.

I'm not sure how long this has been happening, as I seldom drive after dark with the lights on. It happens as much sitting at idle as it does when I am driving. I think the connections are all good, and I wonder if it can be a connection issue by its behavior. It would seem if that was the case, the voltage would drop instead of raise - but I am no expert on it.

I have an alternator and no voltage regulator that is external, so it much be internal to it. There are no problems starting, after sitting for a few weeks at a time - battery seems charged and charging.

Has anyone seen this, or can offer some advice? Maybe a bad alternator or battery? Thanks!

[cdowns]

start by removing bulbs and cleaning the bulbs and sockets for good conductivity then start doin the same for all contacts and grounds/// in a job like this a good wire brush and a tube of dielectric grease to coat the connections can solve alot of the problems

[Andy4639]

Internal regulator is kicking in and out. May be fixing to go out on u are it could be the way it's wired. Did u wire it? If not I would start looking at how it runs.

When the lights appear "normal", the gauge seem to be sitting between 12-13 volts - but in the "bright" phase, the gauge jumps to 16-18 volts.

When driving the truck it should be around 14.5 are so maybe even higher.

12-13 volts is to low.
U may want to check the head light switch also and dim it down.

[OregonNed]

Thanks guys. It is still wired as the previous owner had it. Ill take a look and see how things are wired. Also planned on a good look at the main ground from batt. Should it be grounded to both engine and frame with separate but common cabling on the cable? Such as a cable with two connection points? Wouldn't put it past the alternator too. I've had to replace a few things now. The light switch doesn't seem to have an effect if I jiggle it and try to make something happen
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[Andy4639]

Good grounds are a must on these trucks. Yes ground from battery to motor to frame with heavy duty cables.

The light switch deems the inside lights by turning the knob. I meant if the dash is to bright turn it down with the switch.
Look at the belt also on the alternator could be slipping when slowing down are getting on it hard.

[SCHRUMGMC]

I'll have to post a photo of a cable I noticed that was grounded and my back right brake lights don't work

[OregonNed]

Wasn't just the dash lights -
Tail lights, headlights, side markers, dome light, etc
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[bigmac73]

i had the same problem with my headlights, turned out it was a bad connection inside the fuse block bulkhead connections, took it apart brushed it up and greased it with di eletric grease, and also added another ground cable from engine block to the frame rail , bolted it to the back of the head to frame just used a old battery cable i had in the garage